Optical communication systems provide data exchanges between users by sending optical pulses through optical fibers. Data streams in the electrical domain are modulated and encoded into optical pulses that are received and decoded back into an electrical data stream for a recipient client or user. The optical pulses travel through optical fibers that can carry one or more channels, such as in wavelength division multiplexed networks. Wavelength division multiplexing (WDM) refers to systems that transmit a plurality of channels in a single fiber. Each of the channels corresponds to a predetermined wavelength.
In dense wavelength division multiplexing (DWDM) networks, optical signals having a relatively large number of different wavelengths are multiplexed into a signal fiber. Each wavelength corresponds to a particular channel, each of which has different performance characteristics, such as power, optical signal-to-noise ratio (OSNR), and bit error rate (BER/Q). Performance inconsistencies from channel to channel can result from a variety of factors including non-uniform erbium doped fiber amplifier (EDFA) gain/noise and dispersion tilt over the range of wavelengths. The bandwidth of a fiber can be limited by channel power variations due to diverging attenuation characteristics of the channel wavelengths.
In optical communication systems, optical power is an important parameter in determining the overall system performance. Typically, the system monitors total optical power and per channel power. The total power can be detected by photodetectors in a modular amplifier card (MAC) for controlling fiber amplifiers, such as EDFAs. The per channel power can be measured by channel monitoring cards (CMCs) for balancing and optimizing channel performance. Per channel power adjustments are made to achieve flat gains and/or equal optical signal to noise ratios (OSNR) or Q measurements. The channel power adjustments can be used to tune the transmitters to maintain an optical OSNR for the channels over the bandwidth.
Compensating for channel performance disparities is performed in an attempt to equalize channel performance in a DWDM system. The optical power of each DWDM wavelength launched at the transmitter can be selectively varied and the optimum system performance can be obtained. This is referred to as WDM Power Emphasis or power balancing. Channel balancing is conventionally performed for express wavelengths in relation to optical network source and destination points. The wavelengths added/dropped at an OADN (Optical Add Drop Node) increase the difficulty of channel balance partially due to the difficulty associated with measuring their performance. Also, as network complexity increases, channel balancing becomes increasingly difficult. For example, optical networks are evolving from point-to-point and/or ring configurations to mesh configurations, which render it more challenging to optimize the overall network performance. In addition, channel balancing on a source and destination basis limits the ability of the system to adjust channel power locally in response to isolated conditions or network modifications.
It is therefore desirable to provide in optical networks, a method of channel balancing for both express and add/drop wavelengths in a channel balance section, which may be a whole optical system from source to destination or a sub-system.